Power line communication (PLC), also called mains communication, power line transmission (PLT), broadband power line (BPL), power band or power line networking (PLN), is a term describing a method for using power distribution wires for simultaneous distribution of data. A carrier can communicate voice and data by superimposing an analogue signal over the standard 50 Hz or 60 Hz alternating current (AC). For indoor applications PLC equipment can use household electrical power wiring as a transmission medium.
In order to avoid interferences to amateur radio or other radio services or other external services, frequencies used by these services are notched, i.e. not used for power line communication.
However, power line communication between devices within a PLC system may be interfered by impedance modulating devices outside the PLC system, but connected to the same electrical power wiring, e.g. non linear devices and small switching power supplies, as for instance mobile phone chargers, power supplies for notebooks or energy saving light bulbs. The impedance modulating devices may lead to frequency intermodulations causing inter-carrier-interferences resulting in a reduced transmission quality or lower throughput rates with respect to the power line communication itself and in affecting the transmission spectrum of the PLC system. In particular, transmission signal level may be increased in frequency bands not used for power line communication within the PLC system. Thus, notching as described above is performed less effective than without interferences from impedance modulating devices. This effect is described, for instance, by David Lauder: “Powerline Ethernet Adaptors—how well does ‘notching’ of amateur bands work in practice?”, EMC, Radcom, February 2010.
It is an object of the invention to provide a method for operating a PLC system, which effectively prevents interferences to power line communication within the PLC system itself and to external services caused by impedance modulating devices connected to a mains used by the PLC system for communication. It is furthermore an object of the invention to provide a PLC modem device and a PLC system for performing the method.
The above objects are achieved by the claimed matter according to the independent claims.
Further embodiments are defined in the dependent claims.
Further details of the invention will become apparent from a consideration of the drawings and ensuing description.